TV HD quality?

I have been using my macbook pro and plugging it into my television as my monitor and to play movies. Well i was wondering if using a vga cable can transfer hd quality or does it just transfer the amount of pixels on your computer? I have been looking up HD VGA cables and such and it seems them make them (i think), but is there really a difference in quality. Since my computer does not have an hd monitor i was wondering, because i have a few 1080p movies that i cant tell if they are coming out full quality.

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